Micro-lens substrate, liquid crystal display element having same, and projection-type liquid crystal display device

ABSTRACT

A liquid crystal panel unit ( 2 ) includes, on its side from which light enters, a micro-lens substrate ( 1 ) having: a first micro-lens array including a first lens ( 5 ) for converging, for converging, on aperture sections ( 17 R• 17 G• 17 B) of respective picture elements in a liquid crystal display element, the plurality of the light beams whose respective incident angles are different from one another; and a second micro-lens array having a second lens ( 7 ) for collimating principal rays of the respective light beams. The second lens ( 7 ) is substantially trapezoid so that the lens includes slanted surfaces ( 7   b   •7   b ) directing its convex parts towards the light incident side. With this configuration, it is possible to realize a single-panel mode color-filterless projection-type liquid crystal display device with high light-using efficiency at a low cost, without deteriorating the light-using efficiency.

TECHNICAL FIELD

The present invention relates to a color-filterless projection-typeliquid crystal display device of a single-panel mode, theprojection-type liquid crystal display device having a liquid crystaldisplay element being provided, on its light-incident-side, with twolayers of micro-lens arrays. More specifically, the present inventionrelates to such a projection-type liquid crystal display device, andalso relates to the liquid crystal display element and a micro-lenssubstrate, each of which being mounted in the projection-type liquidcrystal display device.

BACKGROUND ART

A projection type liquid crystal display device has features that aremore advantageous than those of a projection type CRT (cathode-ray tube)display device. For example, a color reproduction range of the liquidcrystal display device is wider than that of the CRT display device.Further, a small size and a light weight of the liquid crystal displaydevice makes it easier to carry the liquid crystal display device.Moreover, since the liquid crystal display device is not affected byearth magnetism, a convergence adjustment is not necessary. Since, it isalso easy to realize a large-size screen, the liquid crystal displaydevice is expected to be a mainstream of home-use image display device.

Among color projection type image display modes utilizing liquid crystaldisplay element, there is three-panel mode in which three panels ofliquid crystal display element are respectively used for three primarycolors, and a single-panel mode in which only one panel of liquidcrystal display element is used. In the three-panel mode, an opticalsystem and three panels of liquid crystal display element areindependently provided. The optical system divides a white beam intothree primary colors, R, G and B, and the respective color beams arecontrolled by the three panels of liquid crystal display element, so asto form an image. Thus, full color display is achieved by opticallysuperimposing images of the respective colors.

Some of the advantages of the three-panel mode are that light beingemitted from a white beam source is efficiently utilized, and that thecolor purity is high. However, it is difficult to reduce the cost andsize of a liquid crystal display device of the three-panel mode, as itrequires the color separation function and the image formation function,which consequently increases the number of components thus complicatingthe optical system of the liquid crystal display device.

On the other hand, the single-panel mode utilizes only one panel ofliquid crystal display element with a color filter pattern shaped inmosaic, stripe, or the like for three primary colors. Images aredisplayed by projecting light on the liquid crystal display element,using an optical system for projection. The single-panel mode issuitable for low-cost and small projection systems, because it requiresonly one panel of liquid crystal display element, and the structure ofits optical system is simpler than one in the three-panel mode.

However, a disadvantage of the single-panel mode is that it can use onlya ⅓ of incident light due to absorption or reflection of light thatoccurs at its color filter. In order to solve this problem, acolor-filterless device, in which two layers of micro-lens arrays areprovided on a light-source facing side of the liquid crystal displayelement has been introduced.

In such a device, dichroic mirrors are arranged in a sector form. Thesedichroic mirrors divide white beam from a white beam source into R, Gand B, and cause the divided beams to enter the first micro-lens arrayat different angles. After passing the first micro-lens array, the lightbeams of the respective colors are refracted by a second micro-lensarray so that the principal rays of the respective colors R, G and Bseparated by the dichroic mirrors become substantially parallel to oneanother. The respective light beams refracted by the second micro-lensarray separately fall on liquid crystal regions driven by signalelectrodes that are independently impressed with color signalscorresponding with R, G and B (e.g. see Japanese Unexamined PatentApplication No. 181487/1995 (Tokukaihei 7-181487; published on Jul. 21,1995)).

The device does not use an absorbing color filter; therefore, not onlythe efficiency of using light improves but also the principal rays ofrespective colors after passing the micro-lens arrays are madesubstantially parallel to one another. As a result, it is possible toprovide remarkably bright images by restraining diffusion of theprincipal rays of the respective colors before they reach a projectionlens, and by preventing decrease in light quantity caused by vignetting.

Nevertheless, the foregoing color-filterless projection type liquidcrystal display device of the single-panel mode, in which the efficiencyof using light is improved, causes a relatively higher cost amongst thedevices of the single-panel mode.

This is attributed to difficulties in manufacturing the secondmicro-lens array, which is one of two micro-lens arrays, for causing theprincipal rays of plural light beams to be parallel to each other.Amongst the plurality of beams incident to a lens of the secondmicro-lens array, a light beam incident to an edge portion of a lens ofthe second micro-lens array is deflected by the second micro-lens arrayso as to be parallel to the principal ray of a light beam incident to acenter of the lens. This requires the lens (the second micro-lens) tohave a large refraction power.

Conventionally, the second micro-lens array has lenses having aspherical surface or a cylindrical surface. The lens having thespherical surface, and the lens having the cylindrical surface bothrequires more thickness in order to obtain the large refraction power.This causes manufacturing of the lens to be extremely difficult, andcauses an increase in the cost.

Further, a trapezoidal lens is sometimes adopted for the secondmicro-lens array (e.g., see Japanese Unexamined Patent Application50081/1997 (Tokukaihei 9-50081; Published on Feb. 18, 1997)). It is easyto increase a thickness of the trapezoidal lens, for increasing therefraction power thereof. However, due to a converged light beamincident to a slanted surface of the trapezoidal lens, a refractiveangle at inside of the light beam and that at outside of the light beamdiffer from each other. This causes a coma aberration and anastigmatism. The occurrence of these aberrations are not preferable,because they deteriorate the efficiency of using light.

The present invention was made in view of the foregoing problems, and itis an object of the present invention to realize a single-panel modecolor-filterless projection type liquid crystal display device with highlight-using efficiency at a low cost, without deterioration inlight-using efficiency.

DISCLOSURE OF INVENTION

In order to achieve the foregoing object, a micro-lens substrate of thepresent invention is a micro-lens substrate provided on a side, of aliquid crystal display element, from which light enters, the liquidcrystal display element being for use in a projection-type liquidcrystal display device, the micro-lens substrate including: (a) a firstmicro-lens array for converging, on a picture element of the liquidcrystal element, a plurality of light beams whose incident angles aredifferent from one another; and (b) a second micro-lens array forcollimating principal rays of the respective light beams, wherein: thesecond micro-lens array has a lens of substantially trapezoid so that:the lens includes (I) a center portion perpendicular to a principal rayof the light beam incident on the center portion and (II) side portionseach having a slanted surface which is slanted at a predetermined anglewith respect to a principal ray of an incident light beam and directsits convex part towards the light incident side, the incident light beambeing incident on each of the side portions.

The second micro-lens array is the one for collimating respectiveprincipal rays of the plurality of the light beams whose respectiveincident angles are different from one another. This requires a largerefraction power for the second micro-lens array. The foregoing secondmicro-lens array is configured to have substantially trapezoidal lensessuch that the center portion of each of the lenses are substantiallyperpendicular including a manufacturing error to the principal ray ofthe light beam incident on the center portion; and the side portions ofeach of the lenses respectively have a slanted surface which is slantedat the predetermined angle with respect to the principal ray of theincident light beam.

With the lens in a shape of trapezoid, it is easier to increase therefraction power by increasing the thicknesses of the lens, as comparedwith a spherical or cylindrical lens. Such an arrangement makes iteasier to manufacture the second micro-lens array, thus making it easierto manufacture the micro-lens substrate than an arrangement having aspherical or cylindrical lens.

If the shape of the lens is mere a trapezoid, the refractive angles ofthe incident light beam with respect to a plane slanted surface becomesdifferent between an inner-side and an outer-side of the light beam.This is because the light beam is a converged light beam. This causes acoma aberration and astigmatism, which consequently deteriorates thelight-using efficiency. In view of the foregoing problem, the shape ofthe lens is not mere a trapezoid, but such a shape that each of theslanted surfaces of the trapezoid directs their convex parts toward theincident light.

Accordingly, it is possible to (I) restrain the difference between therefractive angles of the inner-side and the outer-side of the light beam(converged light beam) incident on the slanted surface, and (II)effectively restrain the coma aberration and astigmatism. This keeps ahigh light-using efficiency, despite of a shape that allows an easymanufacturing process.

As a result, with a provision of the foregoing micro-lens substrate onthe light-incident side of the liquid crystal display element, it ispossible to realize a single-panel mode color-filterless projection-typeliquid crystal display device with high light-using efficiency at a lowcost, without deteriorating the light-using efficiency.

Further, in the second micro-lens array, the convex slanted surface maybe spherical. This allows a highly accurate aberration-correction, thusimproving the light-using efficiency.

Further, in the second micro-lens array, the convex slanted surface maybe cylindrical. Since the surfaces are curved only in one direction, themanufacturing process becomes easy.

Further, in the second micro-lens array, the convex slanted surface maybe aspherical. This allows more highly accurate aberration-correction,thus further improving the light-using efficiency.

Further, in the second micro-lens array, the arched slanted surface maybe in a polyhedral shape having a plurality of surfaces. In this case,it is possible to make working process easier than the case of thespherical or the cylindrical surface.

In order to achieve the foregoing object, a liquid crystal displayelement of the present invention, for use in a projection-type liquidcrystal display device includes the foregoing micro-lens substrate.

As already mentioned, the foregoing micro-lens substrate allows an easymanufacturing of the second micro-lens array, and effectively restrainseffects from aberrations. As a result, by using a liquid crystal displayelement provided with such a micro-lens substrate, it is possible torealize a single-panel mode color-filterless projection-type liquidcrystal display device with high light-using efficiency at a low cost,without deteriorating the light-using efficiency.

Further, in order to achieve the foregoing object, a projection-typeliquid crystal display device of the present invention includes theforegoing liquid crystal display element for use in a liquid crystaldisplay device.

As already mentioned, the foregoing micro-lens substrate allows an easymanufacturing of the second micro-lens array, and effectively restrainseffects from the aberrations. As a result, a single-panel modeprojection type-liquid crystal display device of the present inventionincluding a liquid crystal display element having the foregoingmicro-lens substrate, allows for its production at a low cost withoutdeterioration in its light-using efficiency.

Further, in order to achieve the foregoing object, a projection-typeliquid crystal display device of the present invention is aprojection-type liquid crystal display device having: A) a white beamsource; B) a light beam dividing section for dividing a white beamemitted from the white beam source into a plurality of light beams whoserespective wavelength bands are different from one another; C) a liquidcrystal display element to which the plurality of the light beamsobtained from the light beam dividing section are incident, the lightbeams whose respective incident angles are different from one another;D) two-layers of micro-lens arrays, provided on a light-source side ofthe liquid crystal display element, including a) a first micro-lensarray for converging, on a picture element of the liquid crystalelement, the plurality of the light beams whose respective incidentangles are different from one another, and b) a second micro-lens arrayfor collimating principal rays of the respective light beams; and E) aprojecting section for projecting the plurality of the light beams beingmodulated by the liquid crystal display element, wherein: a lens of thesecond micro-lens array is substantially trapezoid; and the secondmicro-lens array has a lens of substantially trapezoid so that: the lensincludes (I) a center portion perpendicular to a principal ray of thelight beam incident on the center portion and (II) side portions eachhaving a slanted surface which is slanted at a predetermined angle withrespect to a principal ray of an incident light beam and directs itsconvex part towards the light incident side, the incident light beambeing incident on each of the side portions.

As already mentioned, the second micro-lens array is configured to havesubstantially trapezoidal lens such that the center portion of the lensis perpendicular to the principal ray of the light beam incident to thecenter portion; and the side portions of each of the lenses respectivelyhave a slanted surface which is slanted at the predetermined angle withrespect to the principal ray of the incident light beam. Further, theside portions are directing its convex part towards the light incidentside. This configuration allows an easy manufacturing of the secondmicro-lens array, and effectively restrains a coma aberration and anastigmatism.

Accordingly, with the projection type-liquid crystal display device ofthe present invention including a liquid crystal display element havingthe foregoing two-layered micro-lens substrate, it is possible torealize a high light-using efficiency at a low cost, withoutdeteriorating the light-using efficiency.

Additional objects, features, and strengths of the present inventionwill be made clear by the description below. Further, the advantages ofthe present invention will be evident from the following explanation inreference to the drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates an embodiment of the present invention, and is across sectional view illustrating a liquid crystal panel unit providedin a projection-type liquid crystal display device.

FIG. 2( a) is a plane view illustrating a first micro-lens array in amicro-lens substrate provided in the liquid crystal panel unit. FIG. 2(b) is a plane view illustrating a second micro-lens array. FIG. 2( c) isa schematic view illustrating a positional relationship between thefirst and the second micro-lens arrays. FIG. 2( d) is a schematic viewillustrating a relationship between picture elements and second lensesconstituting the second micro-lens array.

FIG. 3 is a perspective view illustrating second lenses constituting thesecond micro-lens array.

FIG. 4 is a schematic view illustrating a configuration of theprojection-type liquid crystal display device.

FIG. 5( a) is an explanatory diagram illustrating how a light beamtravels through a curved slanted surfaces of the second lensconstituting the second micro-lens array. FIG. 5( b) is an explanatorydiagram illustrating how a light beam travels through a plane slantedsurfaces of the second lens constituting the second micro-lens array.

FIG. 6( a) and FIG. 6( b) are explanatory diagrams illustrating how thecurved slanted surfaces of the second lens constituting the secondmicro-lens array are designed.

FIGS. 7( a) to 7(g) are cross sectional views illustrating a method formanufacturing the micro-lens substrate provided in the liquid crystalpanel unit.

FIG. 8 is a schematic view illustrating a configuration of an exposingdevice in which a grayscale mask is used, the exposing device being usedin a process of manufacturing the micro-lens substrate.

FIG. 9 illustrates another embodiment of the present invention, and is across sectional view illustrating a liquid crystal panel unit providedin a projection-type liquid crystal display device.

FIG. 10 is a perspective view illustrating second lenses constituting asecond micro-lens array in a micro-lens substrate provided in the liquidcrystal panel unit.

FIG. 11( a) is an explanatory diagram illustrating h how a light beamtravels through a curved slanted surfaces of the second lensconstituting the second micro-lens array. FIG. 11( b) is an explanatorydiagram illustrating how a light beam travels through a plane slantedsurfaces of the second lens constituting the second micro-lens array.

FIGS. 12( a) to 12(g) are cross sectional views illustrating a methodfor manufacturing the micro-lens substrate provided in the liquidcrystal panel unit.

FIG. 13 is a cross sectional view illustrating a second micro-lens arrayhaving the second lenses whose slanted surfaces have a plurality ofsurfaces so as to form a polyhedral configuration.

BEST MODE FOR CARRYING OUT THE INVENTION

The following examples and comparative examples provide more detaileddescription of the present invention. However, the present invention isnot at all limited to these.

Embodiment 1

The following describes an embodiment of the present invention, withreference to FIGS. 1 to 8.

As shown in FIG. 1, a projection type liquid crystal display device ofthe present embodiment is provided with a liquid crystal panel unit(liquid crystal display element) 2. The liquid crystal panel unit 2includes a plurality of first lenses (first micro lenses) 5 made of ahigh-refractive resin formed below on the bottom side of alight-transmissive protection plate 3 via a planarizing layer 4. Theplanarizing layer 4 is made of a low-refractive resin. Each of the firstlenses 5 configuring the first micro-lens array is an aspherical lens,having a surface directing its convex part toward the incident light.

To a bottom of the first micro-lens array, a light-transmissiveintermediate substrate 6 is attached, and second lenses (second microlenses) 7 made of a high-refractive resin are formed below theintermediate substrate 6. Each of the second lenses 7 configuring asecond micro-lens array is substantially trapezoid, and the second lens7 includes bottom surfaces 7 a on which light is incident. Eachconvex-concave surface of the second micro-lens array is planarized by aplanarizing layer 20 made of a low-refractive resin. A black matrixlayer 8 is formed under the planarizing layer 20. The series of unitsfrom the protection plate 3 to the black matrix layer 8 is hereinafterreferred to as a micro-lens substrate 1.

A transparent electrode 9 made of an ITO (Indium Tin Oxide) or the likeis formed under the black matrix layer 8. Further, an electrode layer 11and a light-transmissive bottom substrate 12 are provided, and a liquidcrystal layer 10 is interposed between the black matrix layer 8 and theelectrode layer 11 having a TFT (Thin Film Transistor) or the like. Withthe transparent electrode 9, the liquid crystal layer 10, and theelectrode layer 11, a pixel section 22 is configured. The black matrixlayer 8 includes aperture sections 17 (17R, 17G, and 17B) correspondingwith respective picture elements of R, G, and B in the pixel section 22.

The following describes further detail of the micro-lens substrate 1. Asshown in FIG. 2( a), the first lenses 5 are formed in a shape ofequilateral hexagon, and are densely arranged (aligned), so as toefficiently transmit light from a later-described white light source 13(see FIG. 4). Here, for example, the first lenses 5 have a verticalpitch of 30 μm, a horizontal pitch of 45 μm, and a curvature radius of15 μmR. The first lenses 5 are so designed that respective focal pointsof the first lenses 5 are positioned nearby the black matrix layer 8.

On the other hand, as shown in FIG. 2( b) and FIG. 3, each of thesubstantially trapezoidal second lenses 7 has a top surface 7 c whoselengthwise side is shorter than that of the bottom surface 7 a. Thesesecond lenses 7 are arranged in a bricklaying manner. The reason why thesecond lens 7 is substantially trapezoids is that slanted surfaces 7 bof the trapezoid are curved surfaces directing their convex parts towardthe incident light. For example, the second lens 7 has the followingdimension. The bottom surface 7 a of the second lens 7 has a dimensionof Width 15 μm×Length 45 μm. The top surface 7 c of the second lens 7has a dimension of Length 15 μm×Width 15 μm. And the height of thesecond lens 7 is 20 μm. Further, the slanted surfaces 7 b of the secondlens 7 are cylindrical.

Further, as shown in FIG. 2( c), the first and the second lenses arearranged such that (I) the first lenses 5 respectively correspond withthe second lenses 7 in a one-to-one manner, and (II) central axes of thefirst lenses respectively match with those of the second lenses.

As illustrated in FIG. 2( d), the second lenses 7 and the pictureelements of R, G, and B are arranged such that each picture element R issandwiched between its adjacent picture elements B and G in the secondlenses 7. In other words, as illustrated in FIG. 1, the top surface 7 cof the second lens 7 faces an aperture 17R corresponding to the pictureelement R, and the slanted surfaces 7 b respectively face apertures 17Band 17G respectively corresponding to the picture elements B and G.

As illustrated in FIG. 4, an optical system of the projection type (rearprojection type) liquid crystal display device having such a liquidcrystal panel unit 2 includes, a white light source 13, an integrator14, a mirror 16, color-separating mirrors 15, and a projection lens 18,in addition to the liquid crystal panel unit 2.

The white light source 13 is, for example, a halogen light, ahigh-pressure mercury-vapor lamp, a metal halide lamp, or the like.Light from the white light source 13 is evenly distributed and orientedby an integrator such as a fly-eye lens, and is then directed to themirror 16 which directs the incident light being a substantiallyparallel light to the color-separating mirrors 15 where the light isdivided, by color-separating mirrors 15, into R-light, G-light, andB-light. The R-light, G-light, and B-light are directed to the liquidcrystal panel unit 2. At this point, the R-light is directedsubstantially perpendicular to the liquid crystal panel unit 2. TheG-light is directed to the liquid crystal panel unit 2 at apredetermined angle θ, and the B-light is directed to the liquid crystalpanel unit 2 at a predetermined angle θ, but in an opposite direction tothe G-light.

The following describes the beams of the respective colors withreference to FIG. 1. The R-light is refracted and converged by the firstlens 5, and is directed to the second lens 7. A focal point of the firstlens 5 is designed to be positioned nearby a center of the aperture 17Rof the black matrix 8. This allows the R-light incident on the secondlens 7 to be converged nearby the center of the aperture 17R. Here, theR-light enters the bottom surface 7 a of the second lens 7 at rightangles, and is emitted from the top surface 7 c.

Meanwhile, the principal ray of the B-light is directed by one of thecolor-separating mirrors 15 to the liquid crystal panel unit 2 at theangle θ with respect to the principal ray of the R-light. Accordingly,even after passing the first lens 5, the B-light enters the bottomsurface 7 a of the second lens 7 at the angle θ. The B-light is thenemitted from one of the slanted surfaces 7 b of the second lens 7. Bypassing through the second lens 7, the principal ray of the B-light isso refracted as to become substantially parallel to that of the R-light.In short, due to the functions of the first lens 5 and the second lens7, the B-light is converged nearby a center of the aperture 17 b of theblack matrix 8.

The G-light and the B-light are substantially symmetrical with respectto the principal ray of the R-light. The principal ray of the G-light isdirected by one of the color-separation mirrors 15 to the liquid crystalpanel unit 2 at the angle θ in a direction opposite to the R-light θwith respect to the principal ray of the R-light. Accordingly, evenafter passing the first lens 5, the G-light also enters the bottomsurface 7 a of the second lens 7 at the angle θ. The G-light is thenemitted from another one of slanted surfaces 7 b of the second lens 7.By passing through the second lens 7, the principal ray of the G-lightis so refracted as to become substantially parallel to that of theR-light. In short, due to the functions of the first lens 5 and thesecond lens 7, the G-light is converged nearby a center of the aperture17G of the black matrix 8.

The R-light, G-light, and B-light, which have respectively passedthrough the apertures of 17R, 17G, and 17B, are respectively modulatedin the picture elements R, G, and B in the pixel section 22. Then, themodulated lights are projected on a screen 19 through a projection lens18.

In this configuration, the R-light, G-light, and B-light, which aredirected to the liquid crystal panel unit 2, transmit more aperturesections 17 of the black matrix layer 8, and furthermore transmit thepixel section 22, thereby contributing to an improvement in light-usingefficiency. This is because the first lens 5, in the micro-lenssubstrate 1 which is provided on a side of the liquid crystal panel unit2 from which side the light enters, has a converging effect.

The G-light and B-light are directed by the color-separating mirrors 15at the angle of θ with respect to the principal ray of the R-light. Assuch, if greater amount of light is converged by the first lens 5 and ifnothing is done, then diameters of the respective light beams R, G, andB keep expanding, and the projection lens 18 in a subsequent sectioncauses a vignetting. This causes a light-loss no matter how much amountof light the first lens 5 collects. In contrast, according to theconfiguration, the respective principal rays of the G-light and theB-light are corrected so as to be substantially parallel (preferablyparallel) to the principal ray of the R-light. Thus, with the foregoingconfiguration, it is possible to (I) restrain the expansion of the lightbeam which has passed through the liquid crystal panel unit 2, and (II)prevent the light-loss caused by the vignetting due to the projectionlens 18. This works synergistically with the foregoing effect, therebymaking a remarkable improvement in the light-using efficiency.

Further, the effects allow a reduction of the focal length of the firstlens 5. Therefore, it is possible that most of the light beam, which arenot perfectly parallel, from the white light source 13 transmit theaperture sections 17 of the black matrix layer 8. This allows a furtherimprovement in the light-using efficiency.

Furthermore, since the second lenses 7 are substantially trapezoid, itis easier to (I) increase the thickness of the lenses to increase therefraction power and (II) manufacture such lenses, as compared to lenseshaving spherical surfaces or cylindrical surfaces.

If the second lens 7 is mere a trapezoid, the inner-side and the outerside of the light beam (converged light beam) which is incident on aplane slanted surface, differ in their refractive angles. This causes acoma aberration and astigmatism, which consequently deteriorates thelight-using efficiency. In contrast, according to the foregoingconfiguration, the second lens 7 is not mere a trapezoid, but each ofthe trapezoidal slanted surfaces 7 b is a curved surface directing itsconvex part toward the incident light. Accordingly, it is possible to(I) restrain the difference between the refractive angles of theinner-side and the outer-side of the light beam (i.e., the respectiveouter-side and the inner-side of the B-light or the G-light) refractedby the slanted surfaces 7 b, and (II) effectively prevent the comaaberration and astigmatism to keep a high light-using efficiency.

The following describes, with reference to FIG. 5( a) and FIG. 5( b),how the light beam travels through a plane slanted surface and acylindrical slanted surface, respectively, in a case where therefraction index on the light incident side is higher than that on thelight-outgoing side, as is the case with the second lens 7 in themicro-lens substrate 1. FIG. 5( a) illustrates the case where theslanted surface is a cylindrical surface directing its convex parttoward the incident light, and FIG. 5( b) illustrates the case where theslanted surface is a plane surface. Here, the respective refractionindexes are n1<n2, and n3<n4.

As shown in FIG. 5( b), when the light beam converged by the first lens5 is incident on a plane slanted surface 24, an incident angle of a rayL2 on an outer-side of the light beam is smaller than that of aprincipal ray L1, and an incident angle of a ray L3 on an inner-side ofthe light beam is larger than that of the L1. This causes a comaaberration and an astigmatism. On the contrary, as shown in FIG. 5( a),when the light beam which is converged by the first lens 5 is incidenton a cylindrical slanted surface 25 directing its convex part toward theincident light, the incident angle of the ray L2 on the outer-side ofthe light beam and the incident angle of the ray L3 on the inner-side ofthe light beam are closer to that of the principal ray L1, as comparedto the case of the plane slanted surface. Therefore, a coma aberrationor an astigmatism less likely occurs.

As described, in the micro-lens substrate 1 having the two-layeredstructure, the second lenses 7 configuring the second micro-lens arrayare substantially trapezoid, and each of the slanted surfaces 7 b has acurved surface directing its convex part toward the incident light. Thisconfiguration reduces the aberration, and improves the light convergingcharacteristic, while simplifying a manufacturing of the secondmicro-lens array. As a result, a good light efficiency is realized.

The slanted surfaces 7 b of the second lenses 7 can be designed asfollows. First, as shown in FIG. 6( a), assuming that the second lens 7is a trapezoid lens having a plane slanted surface 24, the following areset so that n5<n6 is satisfied and the principal ray of the B-lightbecomes substantially parallel to the principal ray of the R-light: (I)a refraction index n5 of a light-outgoing side with respect to theslanted surface 24; (II) a refraction index n6 of a light incident sidewith respect to the slanted surface 24; and (III) a tilt angle θ1 of theslanted surface 24 with respect to a top surface 26.

Next, as illustrated in FIG. 6( b), a cylindrical surface is set so thatan angle of a tangent line L with respect to a top surface 26 is equalto the tilt angle θ1, while refraction indexes of the light-outgoingside and light-incident side of the slanted surface 25 are above setvalues; i.e., n5 on the light-outgoing side and n6 on the light-incidentside. The tangent line L is a tangent line at a point on the cylindricalsurface, which point corresponds to nearby a midpoint on a line (S1=S2in the figure) extending from the top surface 26. At this point, apoint-O in the figure denotes a center of the cylindrical surfaceforming the slanted surface 25.

Next described is an exemplary method for manufacturing the foregoingmicro-lens substrate 1. FIGS. 7( a) to 7(g) are flow-diagramsillustrating the steps of manufacturing the micro-lens substrate 1.

First, a low-refractive resin 33 to become the planarizing layer 4 isapplied between a transparent substrate 32 to become a protection plate3 and a stumper 31. Then, the low-refractive resin 33 is cured by beingexposed to UV-light irradiated in a direction indicated by the arrows inthe figure (See FIG. 7( a)). Next, the stumper 31 is removed (See FIG.7( b)), and then a transparent substrate 35 to become the intermediatesubstrate 6 is bonded via a high-refractive resin 34 as an adhesivelayer (See FIG. 7( c)).

Then, a high-refractive resin 36 to become the second lens 7, and anegative resist 37 are applied in this order to the transparentsubstrate 35 (See FIG. 7( d)). Then, a process of exposing anddeveloping is carried out by using a later-described grayscale mask (notshown) (see FIG. 7( e)). Then, a shape of the lens is transferred to thehigh-refractive resin 36 by carrying out a dry-etching (see FIG. 7( f)).Then, after carrying out a planarization with respect to thehigh-refractive resin 36 by using a low-refractive resin 38 to become aplanarizing layer 20 (See FIG. 7( g)), the micro-lens substrate 1 isobtained.

Note that, after the steps, a passivation layer and the black matrixlayer 8, are formed on the side of the planarizing layer 20 in themicro-lens substrate 1 (not shown). Then, the bottom substrate 12 havingthe electrode layer 11 is further pasted, and liquid crystal to becomethe liquid crystal layer 10 is filled in a gap between the bottomsubstrate 12 and the micro-lens substrate 1 (not shown). Thus, theliquid crystal panel unit 2 is prepared.

The micro-lens substrate 1 thus prepared has the second lenses 7 whoseslanted surfaces are cylindrical surfaces directing their convex partstoward the incident light as shown in FIG. 3. This allows less comaaberrations and less astigmatisms than the configuration in which theslanted surfaces are the plane surfaces. Thus, the light-usingefficiency is improved.

The following describes an exposure method used for forming the secondlenses 7, the exposure method using the grayscale mask. FIG. 8illustrates a schematic configuration of an exposing apparatus for usein manufacturing the second lenses 7. The exposing apparatus includes: aparallel light source 40 for emitting a parallel beam; fly-eye lens 41;a grayscale mask 42; a collimator lens 43; and an aperture 44. Thereference numeral 45 indicates a micro-lens substrate which is inprocess of being manufactured. In this micro-lens substrate, firstlenses 5 are already formed, and the high-refractive resin 36 and thenegative resist 37 have been applied in this order to the transparentsubstrate 35 to become the intermediate substrate 6 (See FIG. 7( d)).

The grayscale mask 42 is a photomask on which transmittances of awavelength of light (i.e., an i-ray in the present embodiment) for usein the exposure is distributed in accordance with the shapes of thesecond lenses 7. With this exposing apparatus, light quantities aredistributed on the negative resist 37, and the negative resist 37 whosefilm thickness is varied according to the distributed light quantitiesis obtained (See FIG. 7( e)). Then, the second lenses 7 are formed bycarrying out an etching for transferring the pattern to thehigh-refractive resin 36, and the low-refractive resin 38 is applied forplanarizing the layer (FIG. 7( g)).

Here, in the formation of the micro-lens substrate 1, the refractionindexes of the high-refractive resin and the low-refractive resin are1.59 and 1.41, respectively at a wavelength of 588 nm. However, asimilar effect can be obtained with different values of the respectiverefractive indexes, provided that there is a difference between theserefraction indexes. Further, in the case of using a negative resist asin the present embodiment, the transmissivity of the light is set sothat a light quantity is large in a position where the lens needs to bethicker, and that a light quantity is small in a position where the lensneeds to be thinner.

Further, the foregoing method for manufacturing the micro-lens substrate1 simplifies a complicated process of positioning of the first and thesecond lenses 5 and 7. Since the positions of the second lenses 7 aredetermined based on the positions of the first lenses 5, two layers ofthe micro-lens arrays are accurately positioned. As a result, it is alsopossible to easily provide a high quality projection-type liquid crystaldisplay device with high light-using efficiency and without unevenbrightness and/or mixing of colors.

Note that in the present embodiment, the second lens 7 is asubstantially trapezoidal lens whose bottom surface 7 a is provided sothat the light is incident on the bottom surface 7 a. However, thesecond lens 7 is not limited to this as long as each of the slantedsurfaces of the second lens 7 is provided so that the light is incidenton the slanted surface directing its convex part toward the incidentlight. Alternatively, it is possible to use a substantially trapezoidallens, whose bottom surface is provided so that the light goes out of thebottom surface. Such a trapezoidal lens is described in detail inEmbodiment 2.

Further, in the present embodiment, the aspherical lens is used as thefirst lens in order to improve the converging characteristic. However,the same effect can be obtained when using a spherical lens.

Embodiment 2

The following describes another embodiment of the present invention,with reference to FIGS. 9 to 13. Note that a configuration of thepresent invention is the same as that of the embodiment 1 unlessotherwise described in this embodiment. Accordingly, the same symbolsare given to the members that have the same functions as those shown infigures of the foregoing embodiment 1, and the descriptions of thosemembers are omitted here for convenience of explanation.

A projection-type liquid crystal display device of the presentembodiment has the same configuration as that of the projection-typeliquid crystal display device in the embodiment 1, except in that aliquid crystal panel unit 52 is provided instead of the liquid crystalpanel unit (liquid crystal display element) 2.

As shown in FIG. 9, in the present embodiment, the liquid crystal panelunit 52 of the projection-type liquid crystal display device includes amicro-lens substrate 51. A light-transmissive bottom substrate 12 isprovided under the micro-lens substrate 51. The light-transmissivebottom substrate 12 is arranged so that a transparent electrode 9 madeof an ITO or the like, a liquid crystal layer 10, and an electrode layer11 including a TFT or the like are formed under the micro-lens substrate51 in this order. As is clear from this, the liquid crystal panel unit 2and the liquid crystal panel unit 52 are different from each other inconfigurations of the respective micro-lens substrates.

The micro-lens substrate 51 is arranged so that a plurality of firstlenses (first micro lenses) 5 made of a high-refractive resin areprovided under a light-transmissive protection plate 3 via a planarizinglayer 4 made of a low-refractive resin. Each of the first lenses 5configuring the first micro-lens array is an aspherical lens havingconvex surface directing toward the incident light. The configuration ofthe micro-lens substrate 51 thus explained is the same as that of themicro-lens substrate 1.

A difference between the micro-lens substrate 51 and the micro-lenssubstrate 1 resides in second lenses (second micro-lenses) 57configuring a second micro-lens array. More specifically, the differencebetween the micro-lens substrate 51 and the micro-lens substrate 1resides in their methods for manufacturing the second lenses 57. Thatis, in the micro-lens substrate 1, the high-refractive resin 36 isformed under the light-transmissive intermediate substrate 6 which isattached to the bottom surface of the first micro-lens array, and thesecond lenses 7 are formed by processing the high-refractive resin 36.In contrast, in the micro-lens substrate 51, second lenses 57 are formed(i) by processing a bottom surface, so that the bottom surface has alens shape, of the light-transmissive intermediate substrate 56, whichis attached to the bottom surface of the first micro-lens array, and(ii) by filling a high-refractive resin in the bottom surface thusprocessed. Further, a black matrix layer 8 is formed under the secondmicro-lens array.

As shown in FIG. 10, the second lenses 57 are substantially trapezoid.Each of the second lenses 57 has (I) a bottom surface 57 a from whichthe light goes out and (II) curved slanted surfaces 57 b directing theirconvex part toward the incident light as is the case with the secondlenses 7. Accordingly, the second lenses 7 are substantially trapezoidallenses in which the slanted surfaces 7 b are curved in a concave manner,whereas the second lenses 57 are the substantially trapezoidal lenses inwhich slanted surfaces 57 b are curved in a convex manner. For example,the second lens 57 has the following dimension. The bottom surface 57 aof the second lens 57 is Length 15 μm×Width 45 μm. The top surface 57 cof the second lens 57 is Length 15 μm×Width 15 μm. And the height of thesecond lens 57 is 20 μm. Further, the slanted surfaces 57 b of thesecond lens 7 are cylindrical.

An alignment of the second lenses 57 configuring the second micro-lensarray is the same as that of the second lenses 7 as shown in FIG. 2( b).A positional relationship between the second lenses 57 and the firstlenses 5, and a positional relationship between the second lenses 57 andpicture elements of R, G, and B in the pixel section 22 are also thesame as those of the second lenses 7 illustrated in FIG. 2( c) and FIG.2( d).

In the projection-type liquid crystal display device (rear projectiontype) including such a liquid crystal panel unit 52, an R-light out ofR-, G-, and B-lights which have been separated by a color-separatingmirrors 15, is refracted by the first lens 5, and is converged anddirected to the second lens 57. A focal point of the first lens 5 isdesigned to be positioned nearby a center of the aperture 17R of theblack matrix 8. As such, the R-light incident on the second lens 57 isconverged nearby the center of the aperture 17R. Here, the R-lightenters the second lens 57 perpendicularly to the top surface 57 c, andgoes out of the bottom surface 57 a.

Meanwhile, the principal ray of the B-light is directed by one of thecolor-separating mirrors 15 to the liquid crystal panel unit 52 at theangle θ with respect to the principal ray of the R-light. Accordingly,even after passing the first lens 5, the B-light enters one of theslanted surfaces 57 b of the second lens 57 at the angle θ. The B-lightis then emitted from the bottom surface 57 a of the second lens 57. Bypassing through the second lens 57, the principal ray of the B-light isso refracted as to become substantially parallel to that of the R-light.In short, due to the functions of the first lens 5 and the second lens57, the B-light is converged nearby a center of the aperture 17B of theblack matrix 8.

The G-light and the B-light are substantially symmetrical with respectto the principal ray of the R-light. The principal ray of the G-light isdirected by one of the color-separation mirrors 15 to the liquid crystalpanel unit 52 at the angle θ in a direction opposite to the R-light θwith respect to the principal ray of the R-light. Accordingly, evenafter passing the first lens 5, the G-light also enters the another oneof slanted surfaces 57 b of the second lens 57 at the angle θ. TheB-light is then emitted from the bottom surface 57 a of the second lens57. By passing through the second lens 57, the principal ray of theG-light is so refracted as to become substantially parallel to that ofthe R-light. In short, due to the functions of the first lens 5 and thesecond lens 57, the G-light is converged nearby a center of the aperture17G of the black matrix 8.

Further, as in the micro-lens substrate 1 of Embodiment 1, in themicro-lens substrate 51, since the second lenses 57 are substantiallytrapezoid, it is easier to (I) increase the thickness of the lenses toincrease the refraction power and (II) manufacture such lenses, ascompared to lenses having spherical surfaces or cylindrical surfaces.Further, according to the foregoing configuration, the second lens 57 isnot mere a trapezoid, but each of the trapezoidal slanted surfaces 57Bis a curved surface directing its convex part toward the incident light.Accordingly, it is possible to (I) restrain the difference between therefractive angles of the inner-side and the outer-side of the light beam(i.e., the respective outer-side and the inner-side of the B-light orthe G-light) refracted by the slanted surfaces 57 b, and (II)effectively prevent the coma aberration and astigmatism to keep a highlight-using efficiency.

The following describes, with reference to FIG. 11( a) and FIG. 11( b),how the light beam travels through a plane slanted surface and acylindrical slanted surface, respectively, in a case where therefraction index on the light incident side is higher than that on thelight-outgoing side, as is the case with the second lens 57 in themicro-lens substrate 51. FIG. 11( a) illustrates the case where theslanted surface is a cylindrical surface directing its convex parttoward the incident light, and FIG. 11( b) illustrates the case wherethe slanted surface is a plane surface. Here, the respective refractionindexes are n1<n2, and n3<n4.

As shown in FIG. 11( b), when the light beam converged by the first lens5 is incident on a plane slanted surface 61, an incident angle of a rayL2 on an outer-side of the light beam is smaller than that of aprincipal ray L1, and an incident angle of a ray L3 on an inner-side ofthe light beam is larger than that of the L1. This causes a comaaberration and an astigmatism. On the contrary, as shown in FIG. 11( a),when the light beam which is converged by the first lens 5 is incidenton a cylindrical slanted surface 62 directing its convex part toward theincident light, the incident angle of the ray L2 on the outer-side ofthe light beam and the incident angle of the ray L3 on the inner-side ofthe light beam are closer to that of the principal ray L1, as comparedto the case of the plane slanted surface. Therefore, a coma aberrationor an astigmatism less likely occurs.

As described, in the micro-lens substrate 51 having the two-layeredstructure, the second lenses 57 configuring the second micro-lens arrayare substantially trapezoid, and each of the slanted surfaces 57 b has acurved surface directing its convex part toward the incident light. Thisconfiguration reduces the aberration, and improves the light convergingcharacteristic, while simplifying a manufacturing of the secondmicro-lens array. As a result, a good light efficiency is realized.

The slanted surfaces 57 b of the second lens 57 can be designed as inthe case of the slanted surfaces 7 b of the second lenses 7.

Next described is an exemplary method for manufacturing the foregoingmicro-lens substrate 51. FIGS. 12( a) to 12(g) are flow-diagramsillustrating the steps of manufacturing the micro-lens substrate 1.

First, a low-refractive resin 33 to become the planarizing layer 4 isapplied between a transparent substrate 32 to become a protection plate3 and a stumper 31. Then, the low-refractive resin 33 is cured by beingexposed to UV-light irradiated in a direction indicated by the arrows inthe figure (See FIG. 12( a)). Next, the stumper 31 is removed (See FIG.12( b)), and then a transparent substrate 63 to become the intermediatesubstrate 56 is bonded via a high-refractive resin 34 as an adhesivelayer, the high-refractive resin 34 to become the first lens 5 (See FIG.12( c)).

Then, a negative resist 64 is applied to the transparent substrate 63(See FIG. 12( d)). Then, aforementioned process of exposing anddeveloping is carried out by using aforementioned grayscale mask (notshown)(see FIG. 12( e)). Then, a shape of the lens is transferred to thetransparent substrate 63 by carrying out a dry-etching (see FIG. 12(f)). Then, after filling in the high-refractive resin 64 to become thesecond lens 57 (See FIG. 12( g)), the micro-lens substrate 51 isobtained.

Note that, after the steps, a passivation layer and the black matrixlayer 8, are formed on the side of bottom surface 57 a of the secondlens in the micro-lens substrate 51 (not shown). Then, the bottomsubstrate 12 having the electrode layer 11 is further pasted, and liquidcrystal to become the liquid crystal layer 10 is filled in a gap betweenthe bottom substrate 12 and the micro-lens substrate 51 (not shown).Thus, the liquid crystal panel unit 52 is prepared.

The micro-lens substrate 51 thus prepared has the second lenses 57 whoseslanted surfaces are cylindrical surfaces directing their convex partstoward the incident light as shown in FIG. 10. This allows less comaaberrations and less astigmatisms than the configuration in which theslanted surfaces are the plane surfaces. Thus, the light-usingefficiency is improved.

Here, in the formation of the micro-lens substrate 51, the refractionindexes of the high-refractive resin and the low-refractive resin are1.59 and 1.41, respectively at a wavelength of 588 nm. However, asimilar effect can be obtained with different values of the respectiverefractive indexes, provided that there is a difference between theserefraction indexes. Further, in the case of using a negative resist asin the present embodiment, the transmissivity of the light is set sothat a light quantity is large in a position where the lens needs to bethicker, and that a light quantity is small in a position where the lensneeds to be thinner.

Further, as in Embodiment 1, the foregoing method for manufacturing themicro-lens substrate 51 simplifies a complicated process of positioningof the first and the second lenses 5 and 57. Since the positions of thesecond lenses 57 are determined based on the positions of the firstlenses 5, two layers of the micro-lens arrays are accurately positioned.As a result, it is also possible to easily provide a high qualityprojection-type liquid crystal display device with high light-usingefficiency and without uneven brightness and/or mixing of colors.

Note that in Embodiments 1 and 2, the second lenses 7 and 57 aresubstantially trapezoidal lenses having the cylindrical slanted surfaces7 b and the cylindrical slanted surfaces 57 b directing their convexparts toward the light incident side respectively. However, therespective slanted surfaces 7 b and 57 b are not limited to the specificones as long as the slanted surfaces 7 b and 57 b direct their convexparts toward the light source. For example, the slanted surfaces 7 b and57 b may be spherical, aspherical, or a polyhedral as shown in FIG. 13having multiple-step plane surfaces. Note that FIG. 13 illustrates ashape of the lenses in cases of a low refraction index on the lightincident side, as is the case with the second lenses 57 in themicro-lens substrate 51 of the embodiment 2.

With a polyhedral slanted surfaces 67, it is possible to make themanufacturing process easier than a spherical, an aspherical, or acylindrical surface. This allows a better manufacturing yield. Further,in a case of a configuration, in which the shape of lens approaches acylindrical surface as the number of steps increases. It is needless tosay that this restrains the coma aberration and the astigmatism moreeffectively.

Further, in the second lenses 7 and 57, the top surfaces 7 c and 57 c,on which the R-beam is incident and which corresponds to center portionsare flat plane surfaces. However, the top surfaces 7 c and 57 c are notlimited to the flat plane surfaces, provided that a light beam isincident, perpendicularly with respect to principal rays, on the topsurfaces 7 c and 57 c. For example, the top surfaces 7 c and 57 c may bespherical, cylindrical, or aspherical surfaces. Note, however, thatthicknesses of the second lenses 7 and 57 are preferably thinner interms of simplicity of the manufacturing process. Accordingly, it ispreferable that the top surfaces 7 c and 57 c be plane surfaces.

Further, in the present embodiment, an aspherical lens is used as thefirst lens so as to improve the converging characteristic. However, itshould be noted that the effects of the present invention are notaffected, even if a spherical lens is used.

Further, the projection-type liquid crystal display device of thepresent invention may be expressed as follows. Namely, a projection-typeliquid crystal display device of the present invention is aprojection-type color liquid crystal display device including: A) awhite beam source; B) a light beam dividing section for dividing a whitebeam emitted from the white beam source into a plurality of light beamswhose respective wavelength bands are different from one another; C) aliquid crystal display element being irradiated with the plurality ofthe light beams obtained from the light beam dividing section; D)two-layers of micro-lens arrays, provided on a light-source side of theliquid crystal display element, including a) a first micro-lens arrayfor converging the plurality of the light beams on apertures ofrespective picture elements of the liquid crystal element, the aperturescorresponding to the respective wavelength bands of the light beams, andb) a second micro-lens array for collimating principal rays of therespective light beams; and E) a projecting section for projecting theplurality of the light beams being modulated by the liquid crystaldisplay element, the second micro-lens array having three surfaces of acentral portion and side portions, the central portion being centerportion perpendicular to a principal ray of the light beam incident onthe center portion, the side portions each having a curved surface whichis slanted at a predetermined angle with respect to a principal ray ofan incident light beam.

Further, the configuration may be so adapted that the curvedside-portions have (A) aspherical surfaces on which the light beams areincident, (B) spherical surfaces on which the light beams are incident;or (C) cylindrical surfaces on which the light beams are incident.

The embodiments and concrete examples of implementation discussed in theforegoing detailed explanation serve solely to illustrate the technicaldetails of the present invention, which should not be narrowlyinterpreted within the limits of such embodiments and concrete examples,but rather may be applied in many variations within the spirit of thepresent invention, provided such variations do not exceed the scope ofthe patent claims set forth below.

INDUSTRIAL APPLICABILITY

The present invention is applicable to a color-filterlessprojection-type liquid crystal display device of a single-panel mode,the projection-type liquid crystal display device, in which two layersof micro-lens arrays are provided on a light incident side of a liquidcrystal display element thereof.

1. A micro-lens substrate provided on a light-incident side of a liquidcrystal display element for use in a projection-type liquid crystaldisplay device, the micro-lens substrate including: (a) a firstmicro-lens array having a first micro lens for converging a plurality oflight beams whose incident angles are different from one another onpicture elements of the liquid crystal element respectivelycorresponding to the light beams; and (b) a second micro-lens arrayhaving a second micro lens for collimating principal rays of therespective light beams converged, by the first micro lens, on therespectively corresponding picture elements, wherein: the secondmicro-lens is substantially trapezoid so that: the second micro-lensincludes (I) a center portion perpendicular to a principal ray of thelight beam incident on the center portion and (II) side portions eachhaving a convex slanted surface which is slanted at a predeterminedangle with respect to a principal ray of an incident light beam anddirects its convex part towards the light incident side, the incidentlight beam being incident on each of the side portions.
 2. Themicro-lens substrate as set forth in claim 1, wherein the convex slantedsurface is spherical surface.
 3. The micro-lens substrate as set forthin claim 1, wherein the convex slanted surface is cylindrical.
 4. Themicro-lens substrate as set forth in claim 1, wherein the convex slantedsurface is aspherical.
 5. The micro-lens substrate as set forth in claim1, wherein the convex slanted surface is in a polyhedral shape having aplurality of surfaces.
 6. A liquid crystal display element for use in aprojection-type liquid crystal display device, comprising the micro-lenssubstrate as set forth in claim
 1. 7. A projection-type liquid crystaldisplay device comprising the liquid crystal display element as setforth in claim
 6. 8. A projection-type liquid crystal display devicecomprising: A) a white beam source; B) a light beam dividing section fordividing a white beam emitted from the white beam source into aplurality of light beams whose respective wavelength bands are differentfrom one another; C) a liquid crystal display element to which theplurality of the light beams obtained from the light beam dividingsection are incident, the light beams whose respective incident anglesare different from one another; D) two-layers of micro-lens arrays,provided on a light-source side of the liquid crystal display element,including a) a first micro-lens array having a first micro lens forconverging a plurality of light beams whose incident angles aredifferent from one another on picture elements of the liquid crystalelement respectively corresponding to the light beams, and b) a secondmicro-lens array a second micro lens for collimating principal rays ofthe respective light beams converged, by the first micro lens, on therespectively corresponding picture elements; and E) a projecting sectionfor projecting the plurality of the light beams being modulated by theliquid crystal display element, wherein: the second micro-lens issubstantially trapezoid so that: the second micro-lens includes (I) acenter portion perpendicular to a principal ray of the light beamincident on the center portion and (II) side portions each having aconvex slanted surface which is slanted at a predetermined angle withrespect to a principal ray of an incident light beam and directs itsconvex part towards the light incident side, the incident light beambeing incident on each of the side portions.